This invention relates to mould support arrangements. More particularly, but not exclusively, this invention relates to mould support arrangements in investment casting processes, for example for forming castings as single crystals.
The investment casting of components of turbine engines, for example turbine blades, can be carried out using single crystal casting. The furnaces for such casting have moulds mounted on chill plates. After the metal is poured into the moulds, the chill plate is withdrawn into a cooler part of the apparatus to provide a unidirectional solidification front perpendicular to the main axis of the mould. A starter or seed ensures that the solidification commences as a single crystal which continues to grow as the solidification front rises through the material in the mould so that the component is formed as a single crystal.
A problem associated with single crystal casting techniques is that stray grains can be formed in the solidifying material. The formation of such stray grains inevitably means that the component has to be scrapped. It has been found that the rate of scrap can be kept to an acceptable level by casting batches of components using one, or a small number of moulds. Large furnaces for casting a large number of components would be more economical, but the overall solidification front in such a furnace tends to be non-planar because the material in the moulds at the outside of the chill plates loses heat at a faster rate than the material in the moulds at the centre. As a result, there is a greater propensity for stray grains to form and, consequently, an increase in the rate of scrap.
The phrase xe2x80x9csolidification frontxe2x80x9d used herein is intended to refer to the interface that forms the boundary between the solid and liquid phases of the solidifying material in the moulds.
According to one aspect of this invention, there is provided a mould support arrangement for supporting a plurality of moulds in a casting apparatus having a first zone for introducing molten material into the moulds and a second zone in which the material in the moulds can cool, the mould support arrangement being capable of relative movement from the first zone to the second zone thereby forming a solidification front in the material in each mould, which solidification front moves relatively through the material as the material solidifies, each mould defining a main axis along which the solidification front can move and a plane perpendicular to the main axis at the base of the mould, the mould support arrangement comprising support means to support the moulds such that the aforesaid planes of successive moulds at increasing distances from a central region of the support means are not co-planar with each other, and such that the main axis of each mould extends substantially perpendicular to the solidification front to be formed therein.
In one embodiment, the main axes of the aforesaid successive moulds may be inclined relative to each other.
In another embodiment, the geometry of the support means may be such that the aforesaid successive moulds are arranged at a lower level on the support means than moulds closer to the central region of the carrying means.
According to another aspect of this invention there is provided a mould support arrangement for supporting a plurality of moulds in a casting apparatus having a first zone for introducing molten material into the mould, and a second zone in which the material in the mould can cool, the mould support arrangement being capable of relative movement from the first zone to the second zone thereby forming a solidification front in the material in each mould, which solidification front moves through the material as the material solidifies, each mould defining a main axis along which the solidification front can move, the mould support comprising support means to support the moulds, wherein the geometry of the carrying means is such that the main axes of successive moulds at increasing distances from a central region of the support means are inclined at successively greater angles to each other, and such that the main axis of each mould extends substantially perpendicular to the solidification front to be formed therein.
The successive moulds as aforesaid may be inclined relative to each other by increasing amounts related to the distance of the mould from the central region of the support means. In one embodiment the moulds are inclined inwardly towards the central region of the support means in another embodiment, the moulds are inclined outwardly away from the central region of the support means.
In one embodiment, the support means comprises carrying means having a generally planar support surface. In another embodiment, the support means includes carrying means which may be generally concave.
The support means may include holding means to hold each mould on the carrying means. The holding means may comprise a distribution member which may include engagement means to engage the moulds and hold the moulds in their desired position on the support surface. The distribution member may be adapted to distribute the molten material to each of the moulds. The distribution member may comprise a manifold.
In another embodiment, the carrying means may comprise a plurality of stepped support faces. Successive support faces at increasing distances from the central region of the carrying means are preferably inclined successively more steeply to the horizontal than those closer to or at the central region. The central support face may be generally horizontal. In this embodiment, the carrying means may comprise the inclined stepped faces, and the support means may further include the holding means as described above.
According to another aspect of this invention, there is provided a mould support arrangement for supporting a plurality of moulds in a casting apparatus having a first zone for introducing molten material into the mould, and a second zone in which the material in the mould can cool, the mould support arrangement being capable of relative movement from the first zone to the second zone thereby forming a solidification front in the material in each mould, whereby the solidification front moves through the material as the material solidifies, each mould having a main axis, the mould support arrangement comprising support means to support the moulds, wherein the geometry of the support means is such that successive moulds arranged at increasing distances from a central region of the support means are arranged at successively lower levels, and such that the main axis of each mould extends substantially perpendicular to the solidification front to be formed therein.
Preferably, the support means comprises carrying means having a generally convex configuration. In one embodiment, the carrying means comprises a generally convex curved surface.
The support means may include holding means to hold each mould on the carrying means. The holding means may comprise a distribution member which may include engagement means to engage the moulds and hold the moulds in their desired position in the support surface. The distribution member may be adapted to distribute the molten material to each of the moulds. The distribution member may comprise a manifold.
In another embodiment, the carrying means comprises a plurality of stepped support faces. Successive support faces at increasing distances from the central region of the carrying means may be arranged at successively lower levels. Each of said stepped faces is preferably substantially horizontal.
In this embodiment, the support means may further include the holding means as described above.
The carrying means may include a chill plate. Supply means may be provided to supply a cooling fluid to the chill plate. Discharge means may also be provided to discharge said cooling fluid from the chill plate.
According to another aspect of this invention, there is provided casting apparatus comprising a mould support arranged as described above, a first zone for introducing molten material into the mould, and a second zone in which the material in the mould can cool, means for moving the mould support arrangement from the first zone to the second zone to effect solidification of the material in the mould.
According to another aspect of this invention there is provided a casting method comprising providing a mould support arrangement having support means for supporting a plurality of moulds, supporting a plurality of moulds by the support means, each mould defining a main axis along which the solidification front can move and a plane perpendicular to the main axis at the base of the mould, the mould being supported by the support means such that the said planes are not co-planar, and such that the main axis of each mould extends substantially perpendicular to a solidification front to be formed therein, introducing a molten material into the mould, cooling the moulds and the molten material to form the solidification front in the material in each mould, whereby the solidification front moves through the material as the material solidifies perpendicular to the main axis of each mould.
According to another aspect of this invention, there is provided a casting method comprising providing a mould support arrangement having support means for supporting a plurality of moulds, supporting a plurality of moulds by the support means, such that successive moulds at increasing distances from a central region of the support means are inclined at successively greater angles to each other, each mould defining a main axis along which the solidification front can move, and each mould being supported by the support means such that the main axis of each mould extends substantially perpendicular to a solidification front to be formed therein, introducing a molten material into the mould, cooling the moulds and the molten material to form the solidification front in the material in each mould, whereby the solidification front moves through the material as the material solidifies perpendicular to the main axis of the mould.
According to another aspect of this invention, there is provided a casting method comprising providing a mould support arrangement having support means for supporting a plurality of moulds, supporting a plurality of moulds by the support means, such that successive moulds arranged from increasing distances from a central region of the support means are arranged at successively lower levels, each mould defining a main axis along which the solidification front can move, and each mould being supported by the support means such that the main axis of each mould extends substantially perpendicular to a solidification front to be formed therein, introducing molten material into the mould, cooling the moulds and the molten material to form the solidification front in the material in each mould, whereby the solidification front moves through the material as the material solidifies perpendicular to the main axis of each mould.